In an engine having a plurality of cylinders (multicylinder engine) such as a diesel engine, a difference in fuel injection amount between the cylinders can be caused by aging deterioration of fuel injection devices (injectors) provided in the cylinders or individual differences therebetween. The difference in fuel injection amount between the cylinders is demonstrated as fluctuations of engine revolution speed such that the engine revolution speed attained when combustion takes place in each cylinder is different for each cylinder.
In order to inhibit such fluctuations of engine revolution speed occurring among the cylinders, correction of fuel injection amount among the cylinders is performed by increasing or decreasing the fuel injection amount in each cylinder in response to fluctuations of engine revolution speed among the cylinders (see Japanese Patent Application Laid-open No. 2001-349243).
For example, when multistage injection (main injection, sub-injection) is implemented in one cycle, a basic injection amount of main injection and a basic injection amount of sub-injection (pilot injection, post injection) are calculated according to the engine operation state, and an inter-cylinder correction amount for conducting increase-decrease correcting the fuel injection amount in each cylinder is calculated for each cylinder according to a difference in engine revolution speed detected between the cylinders,
(Correction A) correction of fuel injection amount (main injection, sub-injection) among the cylinders is performed by distributing the inter-cylinder correction amounts of cylinders to main injection and sub-injection according to the basic injection amount of main injection and sub-injection, or
(Correction B) correction of fuel injection amount (only main injection) among the cylinders is performed by adding all the inter-cylinder correction amounts of cylinders to the basic injection amount of main injection.